1. Field of the Invention
The present invention relates to methods for treating water so as to control microbial contamination and to provide water that is both safe to drink as well as free of unpleasant tastes and odors.
2. Background and Prior Art
Methods of producing high quality drinking water in a portable unit by condensation of dew from ambient air are well known in the art. For example, U.S. Pat. No. 5,669,221 issued to LeBleu et al on Sep. 23, 1997, and U.S. Pat. No. 5,845,504 issued to LeBleu on Dec. 8, 1998, teach a portable non-attended potable water generator enclosed in a decorative case. U.S. Pat. No. 5,553,459 issued to Harrison on Sep. 10, 1996, similarly teaches a water-making apparatus which produces potable water from moisture in the air.
Without satisfactory disinfection of drinking water, numerous problems can result. For example, the typhoid and cholera epidemics which were common throughout American cities in the last century were caused by poor disinfection. The Environmental Protection Agency's Science Advisory Board concluded in 1990 that exposure to microbial contaminants such as bacteria, viruses, and protozoa (e.g., Giardia lamblia and Cryptosporidium) was likely the greatest remaining health risk management challenge for drinking water suppliers.
It has also been recently learned that there are specific microbial pathogens, such as Cryptosporidium, that are highly resistant to traditional disinfection practices. In 1993, Cryptosporidium caused 400,000 people in Milwaukee to experience intestinal illness. More than 4,000 were hospitalized, and at least fifty deaths have been attributed to the disease. There have also been cryptosporidiosis outbreaks in Nevada, Oregon, and Georgia over the past several years. Because of these problems, disinfection has long been recognized as an essential part of the art of producing drinking water. One of the more troubling problems with producing high-quality drinking water from condensation, yet one of the most important, concerns the control of microbial contamination.
There are currently two main commercial ways of treating microbial contamination in drinking water: chlorine and ultraviolet light.
Chlorine is the standard form of treatment used in municipal water treatment systems. However, chlorine is a toxic substance and must be used under strict controls which would be difficult to implement in a portable, unattended device. Chlorine also imparts an unpleasant taste to water, and can react with naturally-occurring materials in the water to form unintended organic and inorganic byproducts which may pose health risks. Oxidizing agents stronger than chlorine—such as ozone or iodine—can also be used, but these are also difficult to implement, may impart unpleasant taste, and can cause the formation of halogenated organic compounds.
Ultraviolet (UV) lights have become the main treatment method for rural residential and commercial systems, and the previously-referenced patents to LeBleu and Harrison teach the control of microbial contamination in water collected from condensation by employing a bacteriostatic loop employing UV light. UV light has a number of practical difficulties, however, such as the difficulty of determining the correct size of the UV light and problems associated with contamination. Levels of water hardness, iron, manganese, humic and fumic acid, tannins and other materials must be minimal to avoid staining on the lamp's internal sleeve which can shield bacteria from the UV rays. Most importantly, UV light has been found to be ineffective for use with water produced from condensation. Although the reason is not precisely known, it is perhaps because the pathogens involved are dissimilar from those found in natural water where UV light has been found to be more effective.
In addition to the methods of disinfection which rely on chlorine or UV light, a number of other methods of disinfection have been proposed. The use of filtration has been proposed, as discussed in U.S. Pat. No. 3,242,073, although this would not be practical in an unattended device.
The use of electrical water purification using an ionization chamber or chambers and electrodes of various alloys, including silver and copper, has been proposed to control algae and bacteria. Prior patents dealing with the problem of electrical water purification include U.S. Pat. No. 4,525,253 issued to Hayes et al on Jun. 25, 1985. The '253 patent teaches the use of electrodes of a copper/silver/nickel alloy. The reference, which is contemplated mainly for swimming pools and other outdoor water storage areas, is directed to removal of algae and bacteria without the use of chlorine; however, the presence of silver in drinking water may lead to health problems. As does the '253 patent, U.S. Pat. No. 4,680,114 issued to Hayes on Jul. 14, 1987, and U.S. Pat. No. 6,207,060 issued to McKay on Mar. 27, 2001 teach the use of silver and copper/silver alloyed electrodes, or copper or zinc electrodes. U.S. Pat. Nos. 4,263,114 & 4,328,084 issued to Shindell disclose the use of electrodes to destroy organic matter, especially in swimming pools and spas. However, the addition of excess sodium to drinking water may be detrimental to human health.
Treatment of household drinking water by passing the water through a bed of activated charcoal impregnated with or having oligodynamic silver or other bactericide adsorbed thereon is known from the prior art. For example, U.S. Pat. No. 2,595,290, patented May 6, 1952, U.S. Pat. No. 3,242,073 patented Mar. 22, 1966, U.S. Pat. No. 3,268,444, patented Aug. 27, 1968, U.S. Pat. No. 3,585,130, patented Jun. 15, 1971, and the references cited therein. In addition, the National Aeronautics and Space Administration has conducted experiments and constructed apparatus for treating spacecraft water using silver ions for biocidal and virucidal purposes. Reference to this work is cited in U.S. Pat. No. 4,198,296, and teaches the biocidal and virucidal effects of silver ions in a very pure distilled or deionized water.
There is a need for a simple, inexpensive method and composition for reducing microbial contamination of water, including water produced from condensation. Such should preserve the taste and quality of the water while being inexpensive and capable of simple, unattended operation.